{SA} 4.0 was released while .NET 4.0 was still in beta. It therefore does not correctly identify the final version of .NET 4.0

The download Chris linked above is the installer for {SA} 4.2, which does correctly identify .NET 4.0.

Please note that there are a small number of bugs in {SA} 4.2, which were corrected in {SA} 4.3. If you are affected by any of these bugs, please email support@red-gate.com, and ask for the {SA} 4.3 installer instead.